Last Updated Jul 31, 2011 1:21 PM EDT
A third defendant is FriendFinder Inc. (FFN), which owns FacebookofSex.com. (That suit is slightly different because FFN seems highly unlikely to get away with marketing a business that uses the exact word "Facebook.")
If Facebook gets its way in the other suits it may end up preventing any other company from marketing products in which the "-book" is used as a suffix in a trademark. That could cause problems for hundreds of brands and companies, including Red Book, Blue Book, and MyYearBook, which was just sold for $100 million.
In its suit against Teachbook, Facebook argues that the name and purpose of the site are confusing because they are too similar to Facebook. Teachbook responded that when Facebook itself was challenged by a company called Factbook, Facebook argued that the two names were too dissimilar to be confusing:
Facebook's Complaint is directly contradicted by the admissions it made just two months after originally filing suit against Teachbook in California. Facebook defended itself in a challenge by "Factbook" by arguing that the marks "Facebook" and "Factbook" look and sound so different that "likelihood of confusion -- can be clearly excluded."Among the hundreds of "-book" companies registered with the U.S. Patent and Trademark Office are Handbook, Portbook, Timebook, Best Book, Black Book, Homebook, Matchbook, Monsterbook, MyBook, and PlayBook.